I'm Making acoustic panels to treat my home studio and plan to use mineral wool or fibreglass insulation to do so. Likely Owen's Corning 703 or something marketed as safe insulation like Bradford Sound Soundscreen or Roxul Safe n' Sound. Regardless of how safe salespeople market these fibrous materials I still want to seal in this material, which leads to the questions:

What material can I wrap around the insulation in order to trap the fibrous particles in but still allow sound to pass?

Is there some kind of measurement that I should be looking for such as stitching density?

I can't find any data about the size of the particles for fibreglass or mineral wool. One company uses a material called Micromesh but provides no data about it:

2 Answers
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You would do fine using simple burlap. Given the wavelengths of the signal that must pass through, cotton fibers will pose no problem. They are also considerably smaller than the coarse fibers found in commercial acoustic panels. In fact, any material used as speaker cover would work for your application. Incidentally, fiberglass is a very hard and acoustically very reflective material. You may do better with a panel of dense open cell, soft urethane-based foam; they may be found at a local craft store.

Thanks! Please explain how you arrived at the conclusion burlap is tight enough to not allow glass fibres to pass? Data would be greatly appreciated as I'm trying to source it. FYI your information regarding sound absorption is incorrect. The wavelength of low frequency sounds are in the magnitude of metres. Fortunately it is not the determining factor for whether a material is permeable for sound. The sound absorption coefficients for rock wool and fibre glass are some of the highest per unit weight out of any available material and this is relatively uniform across the frequency spectrum.
– Luke AllisonJan 9 '17 at 6:53

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engineeringtoolbox.com/particle-sizes-d_934.html provides some information on various particle sizes, and suggests glass wool fibers to be around 1000 microns in size. I'm not able to find a great resource on what size particle burlap will let through (cecor.net/sump-sharks-filters suggests their filter made out of burlap is blocks >500 microns), but keep in mind that -- unlike with a typical filter -- nothing in a bass trap is actively pushing the fibers through the containing membrane.
– Robert NubelApr 19 '17 at 18:05

If you didn't buy the 703 yet, check out Applegate's cotton acoustic panels. Since cotton is harmless there's no need to cover them plus they're rigid enough to use completely by themselves with no frame.